Semiconductor device and method of manufacturing the same

ABSTRACT

In manufacturing a semiconductor device, static electricity is generated while contact holes are formed in an interlayer insulating film by dry etching. Damage to a pixel region or a driving circuit region due to travel of the static electricity generated is prevented. Gate signal lines are spaced apart from each other above a crystalline semiconductor film. Therefore a first protective circuit is not electrically connected when contact holes are opened in an interlayer insulating film. The static electricity generated during dry etching for opening the contact holes moves from the gate signal line, damages a gate insulating film, passes the crystalline semiconductor film, and again damages the gate insulating film before it reaches the gate signal line. As the static electricity generated during the dry etching damages the first protective circuit. the energy of the static electricity is reduced until it loses the capacity of damaging a driving circuit TFT. The driving circuit TFT is thus prevented from suffering electrostatic discharge damage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for improving theproductivity of a semiconductor device, in particular, to a techniquefor preventing electrostatic discharge damage to a switching elementsuch as a thin film transistor (TFT).

The term semiconductor device herein generally refers to a device thatutilizes semiconductor characteristics for functioning the device.Accordingly, electro-optical devices (hereinafter referred to as displaydevices), semiconductor circuits, and electronic equipment are allsemiconductor devices.

2. Description of the Related Art

A technique for manufacturing a TFT comprising a semiconductor thin film(with a thickness of several hundreds to several thousands nm) formed ona substrate having an insulating surface has recently been developed.TFTs are applied to various semiconductor devices such as integratedcircuits (ICs) and electro-optical devices, and quick development ofTFTs as switching elements of the display devices or the like isdemanded.

Recent semiconductor devices are finding their uses expanding asmonitors, televisions, and the display devices for portable terminals.Accordingly, mass production of the semiconductor devices has becomecommon.

FIG. 18 is a diagram showing an example of the entire circuit structureof a conventional semiconductor device. A large number of pixel cellsare arranged in rows and columns, forming a pixel cell array in a pixelregion 1701. Each of the pixel cells comprises a TFT, a transparentpixel electrode, a liquid crystal, and a capacitor storage.

A gate signal line side driving circuit 1711 comprises a shift registercircuit 1707, a level shifter circuit 1708, a buffer circuit 1709, and aprotective circuit 1710.

A source signal line side driving circuit 1712 comprises a shiftregister circuit 1702, a level shifter circuit 1703, a buffer circuit1704, a sampling circuit 1705, and a pre-charge circuit 1706. Also, thepre-charge circuit 1706 may be positioned so as to face the shiftregister circuit 1702, the level shifter circuit 1703, the buffercircuit 1704, and the sampling circuit 1705 with the pixel region 1701interposed therebetween.

In this semiconductor device, a crystalline semiconductor film is formedon an insulating surface, a gate insulating film is formed on thecrystalline semiconductor film, and a gate electrode is formed on thegate insulating film in order to fabricate the thin film transistors.The thin film transistors are then covered with an interlayer insulatingfilm, and contact holes are formed in the interlayer insulating filmthrough dry etching and a metal wiring line is formed to electricallyconnect the thin film transistors with one another.

The above semiconductor device manufacturing process is characterized inthat the pixel region 1701, the gate signal line side driving circuit1711, and the source signal line side driving circuit 1712 aresimultaneously formed through the same steps.

A description will be given with reference to FIGS. 19A to 19C on amethod of manufacturing the conventional circuit, electrostaticgeneration, and damage to TFTs by static electricity. Crystallinesemiconductor films 1803 and 1804 are formed first on an insulatingsurface. Next, an insulating film 1805 is formed so as to cover thecrystalline semiconductor films 1803 and 1804. A gate signal line 1806is then formed on the insulating film 1805. Through these three steps, apixel TFT 1801 and a driving circuit TFT 1802 are formed simultaneously.(FIG. 19A)

An interlayer insulating film 1807 is formed so as to cover the pixelTFT 1801 and the driving circuit TFT 1802. In order to connect the pixelTFT 1801 to the driving circuit TFT 1802 electrically, contact holes1808 and 1809 are formed by dry etching. It has been confirmed thatstatic electricity is generated during the dry etching step, and thatthe generated static electricity moves from one contact hole to the gatesignal line. An arrow shown in FIG. 19B indicates the movement of thestatic electricity generated in the contact hole of the pixel TFT towardthe driving circuit TFT through the gate signal line. Reaching thedriving circuit TFT, the static electricity damages the gate insulatingfilm of the driving circuit TFT and then moves to the crystallinesemiconductor film 1803. The driving circuit TFT 1802 is thus damaged bystatic electricity. (FIG. 19B) The conventional circuits are not capableof preventing damage to TFTs by static electricity that is generated andmoves as described above.

FIG. 20 shows electrostatic discharge damage to a TFT near a pre-chargecircuit in a conventional circuit. Static electricity generated in apixel region moves along a source signal line to a contact hole 1903 onthe upper end of the pixel region. The static electricity then moves toa contact hole 1904 in a drain portion of the pre-charge circuit. Fromthe contact hole 1904 in the drain portion of the pre-charge circuit,the static electricity moves to a first signal line 1905 of thepre-charge circuit and then to a second signal line 1906 of thepre-charge circuit.

When the static electricity moves from the contact hole 1904 in thedrain portion of the pre-charge circuit to the first signal line 1905 ofthe pre-charge circuit. an insulating film is damaged to break thepre-charge circuit. The conventional circuits are not capable ofpreventing damage to pre-charge circuits by static electricity that isgenerated and moves as described above.

Electrostatic discharge damage as described above may lead to displaydefects such as line defect and dot defect in panel display by asemiconductor device, thereby lowering its yield and reliability.

Upon manufacturing a semiconductor device, minute processing is requiredand dry etching that can provide excellent minute processing isindispensable especially upon forming a contact hole with a diameter of3 μm in an interlayer insulating film.

A dry etching process includes the following steps (1) through (6) andthe steps (2) through (6) are repeated.

(1) An etching gas (e.g., XeF₂ or CF₄) is introduced into a vacuumchamber and a high frequency voltage is applied between an upperelectrode and a lower electrode to generate plasma.

(2) Reactive ions having positive electric charge from the generatedplasma enter a surface of the interlayer insulating film at a rightangle.

(3) The reactive ions adsorb to the surface of the interlayer insulatingfilm.

(4) The reactive ions that has adsorb ed to the surface of theinterlayer insulating film react thereon to produce a reaction product.

(5) The reaction product leaves from the surface of the interlayerinsulating film.

(6) The reaction product that has left from the surface of theinterlayer insulating film is discharged.

Electrostatic generation is a result of separating positive electriccharge and negative electric charge from each other by a mechanicaleffect and therefore takes place between the surfaces of solids orbetween the surfaces of a solid and a liquid. Static electricity isgenerated also when a gas separates a solid surface and a liquid surfaceor when a solid or a liquid contains an ionized gas. Then staticelectricity could be generated in the above steps (3) and (5) andelectrostatic generation cannot be avoided.

When a contact hole is opened in an interlayer insulating film throughdry etching in particular, electrostatic discharge damage that takesplace between the contact hole and a gate signal line is so great thatsilicon eliminates. The static electricity in this case is oftenobserved to move from a contact hole to another contact hole.

A long gate signal line has an antenna effect that attracts staticelectricity and electrostatic discharge damage takes place at both endsof the gate signal line.

Against electrostatic discharge damage, the conventional circuit isprovided with a protective circuit 1710 that is placed in the gatesignal line side driving circuit 1711. However, the protective circuit1710 is the type that functions after a metal wiring line is formed andtherefore has no effect of preventing damage to the TFT by staticelectricity generated when the contact holes are opened in theinterlayer insulating film as a step included in the TFT manufacturingprocess. The static electricity thus moves along the gate signal line tothe gate electrode of the TFT and damages the gate insulating film therebefore moving to the source signal line from a source or drain region ofthe TFT. In the manner described above static electricity damages theTFTs in the gate signal line side driving circuit 1711 and in the pixelregion 1701.

The static electricity generated in the pixel region during the dryetching for opening the contact holes in the interlayer insulating filmfurther moves from the contact hole at the upper end of the pixel region1701 to the contact hole in the drain portion of the pre-charge circuit1706. Then the static electricity moves to the first signal line of thepre-charge circuit 1706 and to the second signal line of the pre-chargecircuit. As the static electricity moves from the contact hole in thedrain portion of the pre-charge circuit 1706 to the first signal line ofthe pre-charge circuit 1706, it damages the insulating film.

As described above, the conventional semiconductor device circuit is notcapable of preventing damage to the TFTs in the gate signal line sidedriving circuit 1711, the pixel region 1701, and the source signal linedriving circuit 1712 by the static electricity that is generated duringdry etching for opening the contact holes in the interlayer insulatingfilm. This leads to display defects such as line defect and dot defectin panel display of the semiconductor device, thereby lowering yield andreliability.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and an objectof the present invention is therefore to provide a semiconductor devicethat can avoid electrostatic discharge damage and a method ofmanufacturing the semiconductor device.

One of the features of the present invention is that semiconductordevice comprising: a crystalline semiconductor film formed on aninsulating surface; an insulating film formed on the crystallinesemiconductor film; and a first signal line and a second signal linethat partially overlap the crystalline semiconductor film whilesandwitching the insulating film therebetween, wherein the first signalline and the second signal line are connected to each other through ametal wiring line.

According to the above feature, wherein the first signal line and thesecond signal line are spaced apart from each other so that the firstsignal line and the crystalline semiconductor film sandwich theinsulating film while the second signal line and the crystallinesemiconductor film sandwich the insulating film.

According to the above feature, wherein the first signal line and thesecond signal line are gate signal lines.

According to the above feature, wherein the first signal line and thesecond signal line are connected to a gate electrode of a thin filmtransistor constituting a driving circuit or a pixel.

According to the above feature, wherein the crystalline semiconductorfilm contains an impurity element giving an n type or a p typeconductivity.

Another feature of the present invention is that a semiconductor devicecomprising a pixel and a driving circuit, wherein one or more firstprotective circuits are provided between the driving circuit and thepixel or between a second protective circuit and the pixel, the drivingcircuit and the pixel, or the second protective circuit and the pixel,being connected to each other by a gate signal line, and wherein thefirst protective circuits protect the pixel and the driving circuit fromstatic electricity.

Also, another one of features of the present invention is that a methodof manufacturing a semiconductor device comprising steps of: forming acrystalline semiconductor film on an insulating surface; forming aninsulating film on the crystalline semiconductor film; forming aconductive film on the insulating film; patterning the conductive filmto form a gate electrode; forming an interlayer insulating film coveringthe gate electrode forming a contact hole in the interlayer insulatingfilm; and forming a metal wiring line that is electrically connected toa thin film transistor, wherein the method further comprises the stepsof: forming a second crystalline semiconductor film on an insulatingsurface in the step of forming the crystalline semiconductor film;forming an insulating film on the second crystalline semiconductor filmin the step of forming an insulating film; patterning the conductivefilm to form a first gate signal line and a second gate signal line;forming an interlayer insulating film so as to cover the first gatesignal line and the second gate signal line; forming a contact hole inthe interlayer insulating film; and forming a metal wiring line thatelectrically connects the first gate signal line with the second gatesignal line.

Also, another one of features of the present invention is that asemiconductor device comprising a pre-charge circuit, wherein a firstsignal line of the pre-charge circuit is spaced apart from a secondsignal line of the pre-charge circuit, and wherein a contact portion isprovided at an end of the first signal line.

One of the features of the present invention is that a first protectivecircuit is provided in advance in the path through which staticelectricity travels in order to let static electricity do damage thefirst protective circuit and another one of the features of the presentinvention is that a path for static electricity to travel is provided ina pre-charge circuit in advance in order to prevent damage to thepre-charge circuit. Electrostatic discharge damage to a pixel TFT and adriving circuit TFT can be prevented by these methods. Accordingly, inthe one of features, the present invention places a first protectivecircuit for preventing electrostatic discharge damage to a pixel TFT anda driving circuit TFT between a pixel region and a driving circuitregion, or between a pixel region and a second protective circuit. Also,in the pre-charge circuit, an end of a first signal line of thepre-charge circuit is provided apart from an end of a signal line of thepixel region, and a contact hole is formed at the end of the firstsignal line of the pre-charge circuit so as to make generated staticelectricity move to a second signal line of the pre-charge circuitwithout damaging TFTs in the pre-charge circuit.

According to the present invention, the first protective circuit forpreventing electrostatic discharge damage to the pixel TFT and thedriving circuit TFT, and the pre-charge circuit can be formed at thesame time when the thin film transistors of the pixel region and thedriving circuit region are formed, and formed by the same process as themanufacture process of the thin film transistors. Therefore, noadditional manufacturing process is needed.

The first protective circuit in this specification refers to a circuitthat protects a pixel TFT and a driving circuit TFT from staticelectricity generated during a semiconductor device manufacturingprocess. The first protective circuit lets the generated staticelectricity damage itself in order to reduce an energy of the generatedstatic electricity, thereby preventing electrostatic discharge damage tothe pixel TFT and the driving circuit TFT.

Described first with reference to FIGS. 1A to 1C is a method ofpreventing electrostatic discharge damage to a pixel TFT and a drivingcircuit TFT by providing a first protective circuit in the path wherestatic electricity travels, which is generated during dry etching foropening contact holes in an interlayer insulating film, to therebydamage the first protective circuit.

First, crystalline semiconductor films 14, 15, and 16 are formed on aninsulating surface. An insulating film 17 is formed next so as to coverthe crystalline semiconductor films 14, 15, and 16. On the insulatingfilm 17, gate signal lines 18 and 19 are formed. (FIG. 1A)

In the first protective circuit, the gate signal line 18 is spaced apartfrom the gate signal line 19 above the crystalline semiconductor film15, and therefore the gate signal lines 18 and 19 have no electricalconnection when contact holes are opened in an interlayer insulatingfilm 20. Since static electricity generated during dry etching forforming a contact hole 24 cannot move along the gate signal line 19directly, as indicated by an arrow shown in FIG. 1B, the staticelectricity moves from the gate signal line 19; damages the gateinsulating film 17; passes the crystalline semiconductor film 15; andagain damages the gate insulating film 17 before it reaches the gatesignal line 18. A contact hole 21 and the contact hole 24 shown in FIG.1B are reached the semiconductor films 14 and 16, respectively. (FIG.1B)

At a time when the static electricity generated during the dry etchingfor forming the contact holes in the interlayer insulating film 20damages a first protective circuit 13, the energy of the staticelectricity is reduced until it loses the capacity of damaging a drivingcircuit TFT 12. As a result, the driving circuit TFT 12 is thusprevented from suffering electrostatic discharge damage. (FIG. 1B)

At the point illustrated in FIG. 1B, the gate signal lines 18 and 19 arenot connected to each other, and therefore a pixel region is notelectrically connected to a driving circuit region. To connect the pixelregion and the driving circuit region to each other, a metal wiring line26 is formed by a metal wiring line forming process. (FIG. 1C)

Described next is a method of preventing electrostatic discharge damageto a pre-charge circuit by providing in advance a path for staticelectricity generated during dry etching for opening contact holes in aninterlayer insulating film to travel.

A pre-charge circuit is arranged apart from a pixel region in order tomake static electricity generated during dry etching for opening contactholes in an interlayer insulating film move to a first signal line ofthe pre-charge circuit. A contact hole is formed at an end of the firstsignal line of the pre-charge circuit by the pixel region side. As aresult, the static electricity moves from the contact hole at the upperend of the pixel region through the contact hole provided at the end ofthe first signal line of the pre-charge circuit to the first signal lineof the pre-charge circuit. The static electricity has moved to the firstsignal line flows a second signal line of the pre-charge circuit.Electrostatic discharge damage to the pre-charge circuit thus can beprevented.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are diagrams showing a process of manufacturing asemiconductor device with a first protective circuit incorporatedtherein:

FIGS. 2A to 2C are diagrams showing a process of manufacturing asemiconductor device with a first protective circuit incorporatedtherein;

FIGS. 3A and 3B are diagrams showing a process of manufacturing asemiconductor device with a first protective circuit incorporatedtherein;

FIGS. 4A to 4C are diagrams showing a process of manufacturing asemiconductor device with a first protective circuit incorporatedtherein;

FIGS. 5A to 5C are diagrams showing a process of manufacturing asemiconductor device with a first protective circuit incorporatedtherein;

FIGS. 6A to 6C are diagrams showing a process of manufacturing asemiconductor device with a first protective circuit incorporatedtherein;

FIG. 7 is a diagram showing the entire circuit structure of asemiconductor device;

FIGS. 8A and 8B are a diagram showing an embodiment mode in which afirst protective circuit is placed between a pixel region and a drivingcircuit region and a sectional view of the first protective circuit,respectively;

FIGS. 9A and 9B are a diagram showing an embodiment mode in which afirst protective circuit is placed between a pixel region and a secondprotective circuit and a sectional view of the first protective circuit,respectively;

FIG. 10 is a diagram illustrating a method of preventing electrostaticdischarge damage to a pre-charge circuit by providing a path in thepre-charge circuit so that static electricity travels along the path;

FIG. 11 is a diagram showing an embodiment mode in which firstprotective circuits are placed between a pixel region and a drivingcircuit region;

FIGS. 12A and 12B are a diagram showing an embodiment mode in whichfirst protective circuits are placed between a pixel region and adriving circuit region and a sectional view of the first protectivecircuits, respectively;

FIGS. 13A and 13B are a diagram showing an embodiment mode in which afirst protective circuit is placed between a pixel region and a drivingcircuit region and a sectional view of the first protective circuit,respectively;

FIGS. 14A to 14F are diagrams showing examples of devices utilizing asemiconductor device;

FIGS. 15A and 15B are diagrams showing examples of devices utilizing asemiconductor device;

FIGS. 16A and 16B are diagrams showing a successful example ofpreventing electrostatic discharge damage to a pre-charge circuit byproviding a path in the pre-charge circuit so that static electricitytravels along the path;

FIGS. 17A to 17C are graphs showing electric characteristics;

FIG. 18 is a diagram showing an example of the entire circuit structureof a conventional semiconductor device;

FIGS. 19A to 19C are diagrams showing a method of manufacturing aconventional circuit, electrostatic generation, and damage to TFTs bystatic electricity; and

FIG. 20 is a diagram showing damage to TFTs by static electricity near apre-charge circuit in a conventional circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[Embodiment Mode 1]

FIG. 8A shows, as an embodiment mode of the present invention, a circuitwith a first protective circuit placed between a pixel region and adriving circuit region. FIG. 8B is an enlarged sectional view of thefirst protective circuit. An embodiment mode of the first protectivecircuit will be described with reference to FIGS. 8A and 8B.

A crystalline semiconductor film 704 is formed on a base film (notindicated by a symbol in FIGS. 8A and 8B), which is formed on a glasssurface. A gate insulating film 705 with a thickness of 10 to 200 nm,preferably, 50 to 150 nm, is formed so as to cover the crystallinesemiconductor film 704. On the gate insulating film 705, gate signallines 706 and 707 are formed to have a thickness of 100 to 400 nm. Thegate signal lines 706 and 707 are spaced apart from each other above thecrystalline semiconductor film 704.

An interlayer insulating film 708 is laid on the crystallinesemiconductor film 704 and the gate signal lines 706 and 707. Contactholes are formed in the interlayer insulating film 708 and a metalwiring line 709 is formed so as to electrically connect the gate signallines 706 and 707. The metal wiring line 709 electrically connects apixel region 703 to a driving circuit region 701 when the firstprotective circuit is damaged by static electricity.

Static electricity generated through dry etching for opening the contactholes in the interlayer insulating film in the pixel region 703 movesfrom the gate signal line 706 toward the driving circuit region 701.When the contact holes are opened in the interlayer insulating film, thegate signal lines 706 and 707 are spaced apart from each other.Accordingly, the static electricity that has traveled along the gatesignal line 706 damages the gate insulating film 705 before moving tothe crystalline semiconductor film 704. Then the static electricityagain damages the gate insulating film 705, and moves through the gatesignal line 707 to the driving circuit region 701.

The static electricity damages a first protective circuit 702 to reduceits energy until the static electricity loses the capacity of damagingthe driving circuit region 701. Therefore the static electricity causesno damage upon reaching the driving circuit region 701. Electrostaticdischarge damage to the driving circuit region 701 is thus prevented.

On the other hand, static electricity that is generated through dryetching for opening contact holes in the interlayer insulating film inthe driving circuit region 701 moves from the gate signal line 707toward the pixel region 703.

This static electricity damages the first protective circuit 702 toreduce its energy until the static electricity loses the capacity ofdamaging the pixel region 703. Therefore the static electricity causesno damage upon reaching the pixel region 703. Electrostatic dischargedamage to the pixel region 703 is thus prevented.

Thereafter, the metal wiring line 709 is electrically connected to thegate signal lines 706 and 707 to electrically connect the pixel region703 to the driving circuit region 701.

[Embodiment Mode 2]

FIG. 9A shows as an embodiment mode of the present invention a circuitwith a first protective circuit placed between a pixel region and asecond protective circuit. FIG. 9B is an enlarged sectional view of thefirst protective circuit. An embodiment mode of the first protectivecircuit will be described with reference to FIGS. 9A and 9B.

A first protective circuit 802 are arranged interposed between the pixelregion 801 and the second protective circuit 803. The first protectivecircuit 802 has the same structure and function as those of the firstprotective circuit 702, which is interposed between the pixel region andthe driving circuit region in Embodiment Mode 1. The second protectivecircuit 803 comprises a semiconductor film.

Static electricity is generated through dry etching for opening contactholes in an interlayer insulating film in a pixel region 801. The staticelectricity generated moves from a gate signal line 807 toward a secondprotective circuit 803. When the contact holes are opened in theinterlayer insulating film, the gate signal lines 806 and 807 are spacedapart from each other. Accordingly, the static electricity that hastraveled along the gate signal line 807 damages a gate insulating film805 before moving to a crystalline semiconductor film 804. Then thestatic electricity again damages the gate insulating film 805, and movesthrough the gate signal line 806 to the second protective circuit 803.

The static electricity damages the first protective circuit 802 toreduce its energy until the static electricity loses the capacity ofdamaging the second protective circuit 801. Therefore the staticelectricity causes no damage upon reaching the second protective circuit801. Electrostatic discharge damage to the second protective circuit 801is thus prevented.

Thereafter, a metal wiring line 809 is electrically connected to thegate signal lines 806 and 807 to electrically connect the pixel region801 to the second protective circuit 803.

[Embodiment Mode 3]

FIG. 10 shows a pre-charge circuit and circuits in the periphery thereofin accordance with an embodiment mode of the present invention. Anembodiment mode of the pre-charge circuit will be described withreference to FIG. 10.

A pre-charge circuit 901 is spaced apart from a pixel region 902. Thepre-charge circuit has a first signal line 907, which has a contact hole904 at an end on the pixel region side. Also provided are a contact hole905 of the pre-charge circuit. a second signal line 908 of thepre-charge circuit, and a contact hole 906 of the second signal line ofthe pre-charge circuit. The first signal line 907 of the pre-chargecircuit is not directly connected to the second signal line 908 of thepre-charge circuit but electrically connected through a metal wiringline.

Static electricity is generated through dry etching for opening contactholes in an interlayer insulating film in the pixel region 902. Thestatic electricity generated moves from a contact hole 903 of a pixel tothe contact hole 904 of the first signal line of the pre-charge circuit.From the contact hole 904 of the first signal line of the pre-chargecircuit, the static electricity moves to the contact hole 905 of thepre-charge circuit. The static electricity then leaves the contact hole905 of the pre-charge circuit for the contact hole 906 of the secondsignal line of the pre-charge circuit.

While the static electricity moves as described above owing to thecontact hole 904 of the first signal line of the pre-charge circuit, thestatic electricity runs through the first signal line 907 of thepre-charge circuit without flowing into a contact hole 909 of a drainportion of the pre-charge circuit. Therefore damage to the pre-chargecircuit is avoided.

[Embodiment Mode 4]

FIG. 11 shows a circuit in which two first protective circuits 1002 areplaced between a pixel region and a driving circuit region.

Each of the first protective circuits 1002 has the same structure as thefirst protective circuit 702, and static electricity generated throughdry etching for opening contact holes in an interlayer insulating filmis allowed to damage the first protective circuits 1002 to therebyprevent electrostatic discharge damage to a pixel TFT and a drivingcircuit TFT.

With two first protective circuits arranged as shown in FIG. 11, thestatic electricity generated through dry etching for opening contactholes in an interlayer insulating film loses more energy. This makes theelectrostatic discharge damage countermeasure more effective.

[Embodiment Mode 5]

FIG. 12A shows a circuit in which two first protective circuits 1102 areplaced between a pixel region and a driving circuit region. FIG. 12Bshows a sectional view of the first protective circuits 1102.

Each of the first protective circuits 1102 has the same structure as thefirst protective circuit 702, and static electricity generated throughdry etching for opening contact holes in an interlayer insulating filmis allowed to damage the first protective circuits 1102 to therebyprevent electrostatic discharge damage to a pixel TFT and a drivingcircuit TFT.

With two first protective circuits arranged as shown in FIG. 12, thestatic electricity generated through dry etching for opening contactholes in an interlayer insulating film loses more energy. This makes theelectrostatic discharge damage countermeasure more effective.

[Embodiment Mode 6]

FIG. 13A shows a circuit with a first protective circuit 1202 placedbetween a pixel region and a driving circuit region. FIG. 13B is asectional view of the first protective circuit 1202.

Crystalline semiconductor films 1203 and 1204 are formed on a base film(not indicated by a symbol in FIGS. 13A and 13B), which is formed on aglass surface. A gate insulating film 1205 is formed so as to cover thecrystalline semiconductor films 1203 and 1204. On the gate insulatingfilm 1205, gate signal lines 1206 to 1208 are formed. The gate signallines 1206 and 1207 are spaced apart from each other above thecrystalline semiconductor film 1203. The gate signal lines 1207 and 1208are spaced apart from each other above the crystalline semiconductorfilm 1204.

An interlayer insulating film 1209 is laid on the crystallinesemiconductor films 1203 and 1204 and the gate signal lines 1206 to1208. Contact holes are formed in the interlayer insulating film 1209and a metal wiring line 1210 is formed to electrically connect the gatesignal lines 1206 and 1208 to each other. The metal wiring line 1210electrically connects a pixel region 703 to a driving circuit region 701after the first protective circuit is damaged by static electricity.

Similar to the ones in Embodiment Modes 1,2,4, and 5, the firstprotective circuit 1202 reduces the energy of static electricitygenerated through dry etching for opening the contact holes in theinterlayer insulating film to thereby prevent electrostatic dischargedamage to a pixel TFT and a driving circuit TFT.

[Embodiment 1]

A method of manufacturing a semiconductor device that has a firstprotective circuit incorporated therein will be described in detail withreference to FIGS. 2A to 7.

FIG. 7 shows the entire circuit structure of a semiconductor device towhich the present invention is applied. The semiconductor devicecomprises a pixel region 601, a gate signal line side driving circuit612, and a source signal line side driving circuit 613. The gate signalline side driving circuit 612 comprises a shift register circuit 606, alevel shifter circuit 607, a buffer circuit 608, a second protectivecircuit 609, and first protective circuits 611. The source signal lineside driving circuit 613 comprises a shift register circuit 602, a levelshifter circuit 603. a buffer circuit 604. a sampling circuit 605, and apre-charge circuit 610. Polycrystalline silicon TFTs having the GOLDstructure that is an effective hot carrier countermeasure are used forthe shift register circuits 602 and 606, the level shifter circuits 603and 607, and the buffer circuits 604 and 608. On the other hand,polycrystalline silicon TFTs having the LDD structure that is effectivein reducing the OFF current value are used for the pixel region 601 andthe sampling circuit 605 that is a part of the peripheral circuits. Oneof the first protective circuits 611 is placed between the pixel region601 and the buffer circuit 608 whereas the other is placed between thepixel region 601 and the second protective circuit 609. The pre-chargecircuit 610 is interposed between the pixel region 601 and the samplingcircuit 605.

A specific description will be given below with reference to FIGS. 2A to6C on a method of manufacturing the semiconductor device having thecircuit structure described above. FIGS. 2A to 6C are sectional viewstaken along the line A-A′ of FIG. 8A, which is an illustration ofEmbodiment Mode 1.

First, a base film 101 is formed on a glass substrate 100 by plasma CVD.The base film 101 consists of a first layer silicon oxynitride film 101a with a thickness of 50 nm and a second layer silicon oxynitride film101 b with a thickness of 100 nm. The glass substrate 100 used here maybe formed of quarts glass, barium borosilicate glass, aluminoborosilicate glass, or the like. (FIG. 2A) Next, an amorphous siliconfilm 102 with a thickness of 55 nm is formed on the base film 101 (101 aand 101 b) by plasma CVD. Then a nickel-containing solution is held tothe top face of the amorphous silicon film. After the amorphous siliconfilm is subjected to dehydrogenation treatment (at 500° C. for an hour).thermal crystallization (at 550° C. for four hours) and laser annealingtreatment are performed on the amorphous silicon film to change it intoa polycrystalline silicon film 103. (FIG. 2B)

A silicon oxide film 105 with a thickness of 130 nm is formed on apolycrystalline silicon film 104, which is then doped with an impurityelement (boron or phosphorus) in order to control the threshold of TFTs.(FIG. 2C)

The polycrystalline silicon film is patterned next by photolithographyand etching to form semiconductor layers 202 to 204. (FIGS. 3A and 3B)

A gate insulating film 301 that is a silicon oxynitride film formed byplasma CVD to a thickness of 115 nm is formed so as to cover thesemiconductor layers 202 to 204. Formed on the gate insulating film 301by sputtering is a gate electrode film consisting of a 30 nm thick TaNfilm 302 and a 370 nm thick tungsten film 303. (FIG. 4A)

Next, resist patterns 304 to 307 for forming gate electrodes are used asmasks to perform dry etching on the gate electrode film which consistsof a TaN film and a tungsten film and which measures 400 nm in thicknessin total. Tapered gate electrodes are obtained by gradually pulling theresist patterns back during dry etching. (FIG. 4B)

Without removing the resist patterns 304 to 307 after the dry etching,high concentration ion implantation of an n type impurity is carried outas first ion implantation treatment. As a result, high concentrationimpurity regions (n+ regions) 312 to 314 are formed in regions of thesemiconductor layers 203 and 204 that are not covered with gateelectrodes 310 and 311. Conditions for the fist ion implantationtreatment include using phosphorus as the n type impurity, setting thedose to 1.5×10¹⁵ atoms/cm², and setting the acceleration voltage to 80kV. (FIG. 4B)

The gate electrodes are again subjected to dry etching. This time, theinitial resist patterns 304 to 307 are utilized but the etchingconditions are changed so that the gate electrodes receive anisotropicetching. In this etching, the TaN film is etched and recedes and thetungsten film is tapered at a taper angle of nearly 90°. (FIG. 4C)

Then low concentration ion implantation of an n type impurity is carriedout as second ion implantation treatment. The conditions for the secondion implantation treatment include using phosphorus, setting the dose to1.5×10¹⁴ atoms/cm², and setting the acceleration voltage to 90 kV. Inthe second ion implantation treatment. regions covered with the TaN filmare doped with phosphorus through the TaN film and the gate insulatingfilm and, as a result, n−-regions 403 and 404 are formed at positionswhere the regions overlap the gate electrodes. In regions that are notcovered with the TaN film, on the other hand, portions outside the gateelectrodes are doped with phosphorus through the gate insulating film toform—regions 401 and 402. (FIG. 5A)

The next step is photolithography with which a resist aperture is openedin a capacitor storage 522 region in the pixel region by patterningwhile covering the rest with resist patterns 405 and 406. (FIG. 5B)

Using the resist patterns 405 and 406 as masks, high concentration ionimplantation of a p type impurity is carried out as third ionimplantation treatment. In the third ion implantation treatment, thecapacitor storage 522 region receives ion implantation of a p typeimpurity, such as boron, that is an impurity element imparting theconductivity type reverse to the conductivity type of the impurity usedin previous ion implantation. A high concentration impurity region (p+region) is formed in a region 407 that is covered with the TaN film butnot with the gate electrode 311. The third ion implantation region hasalready received ion implantation of phosphorus that is an n typeimpurity. However, the region is doped with boron that is a p typeimpurity element in a concentration of 2×10²⁰ to 2×10²¹ atoms/cm³, andtherefore can function as source and drain regions of a p-channelpolycrystalline silicon TFT. (FIG. 5C)

The resist patterns 405 and 406 are removed and then a siliconoxynitride film with a thickness of 150 nm is formed by plasma CVD as afirst interlayer insulating film 501. The semiconductor layers 202 to204 are subjected to thermal annealing at 550° C. for four hours tothermally activate the impurity elements implanted in the semiconductorlayers. In this embodiment, gettering of nickel used as a catalyst forcrystallization of the semiconductor layers 202 to 204 is done at thesame time the impurity elements are thermally activated. This getteringis for lowering the OFF current value of the TFTs and for improving thefield effect mobility of the TFTs. Through gettering, nickel is moved tothe impurity regions 312 to 314 containing a high concentration ofphosphorus and the nickel concentration is lowered in the semiconductorlayers that are to serve as channel formation regions. With a channelformation region formed in this way, a TFT can exhibit excellentelectric characteristics such as reduced OFF current value. The thermalactivation treatment may be conducted before the first interlayerinsulating film 501 is formed. However, if a wiring line material of thegate electrodes 310 and 311 is weak against heat, it is preferred toform the interlayer insulating film before the thermal activationtreatment as in this embodiment. Then heat treatment is carried out in anitrogen atmosphere containing 3% of hydrogen at 410° C. for an hour, sothat the semiconductor layers 202 to 204 are hydrogenated and danglingbonds thereof are terminated. (FIG. 6A)

On the first interlayer insulating film 501 formed of siliconoxynitride, a second interlayer insulating film 506 is formed to athickness of 1.6 μm from an organic insulating material comprised of anacrylic resin. Thereafter, contact holes are formed throughphotolithography and dry etching to connect two gate signal lines 502and 503 of a first protective circuit 520 to the impurity regions 312,313, and 407, that are the first and third ion implantation regions. Ithas been confirmed that static electricity is generated at this stage.However, the first protective circuit has already been completed and thegenerated static electricity damages the first protective circuit 520.Therefore electrostatic discharge damage to a pixel TFT and a drivingcircuit TFT can be prevented. (FIG. 6B)

Formed next is a metal wiring line 507 for electrically connecting thetwo gate signal lines 502 and 503 of the first protective circuit 520.Connection electrodes 508 and 509 in a pixel region 523 and a connectionelectrode 510 in the capacitor storage 522 are formed at the same timethe metal wiring line 507 is formed. The metal wiring line used here isa laminate consisting of a Ti film 50 nm in thickness and a Al—Ti alloyfilm 500 nm in thickness. The connection electrode 509 is connected tothe impurity region 313 of a pixel TFT 521 whereas the connectionelectrode 510 is connected to the impurity region 407 of the capacitorstorage 522. Next, a transparent electrode film such as an ITO (indiumtin oxide) film is formed to a thickness of 110 nm to form a transparentpixel electrode 511 through photolithography and dry etching. Thetransparent pixel electrode 511 is electrically connected to theimpurity region 313 of the pixel TFT 521 through the connectionelectrode 509. The transparent pixel electrode 511 is electricallyconnected to the impurity region 407 of the capacitor storage 522through the connection electrode 510. (FIG. 6C)

Thus completed is the semiconductor device comprising the firstprotective circuit 520 and the pixel portion 523 that has the pixel TFT521 and the storage capacitor 522.

[Embodiment 2]

FIGS. 16A to 17C show an example of applying the techniques of thepresent invention to a semiconductor device. FIG. 16B is an enlargedview of FIG. 16A.

Static electricity generated in a contact hole {circle around (1)} atthe upper end of a pixel region moves to a contact hole {circle around(2)} that is provided in advance at the lower end of a first signal line{circle around (3)} of a pre-charge circuit. Running along the firstsignal line {circle around (3)} of the pre-charge circuit, the staticelectricity moves from a contact hole {circle around (4)} to a contacthole {circle around (5)} of a second signal line of the pre-chargecircuit and then to the second signal line of the pre-charge circuit.

In a conventional circuit where the contact hole {circle around (2)} isnot provided in the lower end of the first signal line {circle around(3)} of the pre-charge circuit, the static electricity generated in thepixel region moves from the contact hole {circle around (1)} at theupper end of the pixel region to a contact hole {circle around (2)}′ ina drain portion of the pre-charge circuit, and then travels along thefirst signal line {circle around (3)} of the pre-charge circuit to reachthe contact hole {circle around (5)} of the second signal line of thepre-charge circuit and to enter the second signal line of the pre-chargecircuit from there. The pre-charge circuit is damaged by the staticelectricity when it moves from the contact hole {circle around (2)}′ ofthe drain portion of the pre-charge circuit to the first signal line{circle around (3)} of the pre-charge circuit.

FIGS. 17A to 17C are graphs proving, through electric characteristicmeasurement, that the techniques of the present invention are successfulin preventing electrostatic discharge damage to the pre-charge circuiteven though the static electricity generated in the pixel region runningabout the pre-charge circuit.

There is a trace of static electricity running in the 1280-th stageaddress (FIG. 17B) but electric characteristics thereof are no differentfrom those of the 1279-th stage address (FIG. 17A) and the 1281-th stageaddress (FIG. 17C) where no trace of static electricity movement isfound. This shows that the countermeasure against the electrostaticdischarge damage is working well.

The above results proves that the present invention is capable ofpreventing electrostatic discharge damage to a pre-charge circuit andimproving the yield and reliability of a semiconductor device.

[Embodiment 3]

The active matrix substrate and the liquid crystal display devicefabricated by implementing the present invention can be utilized forvarious electro-optical devices. Namely, the present invention can beimplemented onto all of the electronic devices that incorporate suchelectro-optical devices as a display portion.

Following can be given as such electronic devices: video cameras;digital cameras; projectors (rear type or front type); head mounteddisplays (goggle type displays); car navigation systems; car stereo;personal computers; portable information terminals (mobile computers,portable telephones or electronic books etc.) etc. Examples of these areshown in FIGS. 14 and 15.

FIG. 14A is a personal computer which comprises: a main body 1301; animage input section 1302; a display section 1303; and a key board 1304.The present invention can be applied to the image input section 1302,the display section 1303 and other driver circuits.

FIG. 14B is a video camera which comprises: a main body 1305; a displaysection 1306; a voice input section 1307; operation switches 1308; abattery 1309 and an image receiving section 1310. The present inventioncan be applied to the display section 1306, a voice input section 1307and other driver circuits.

FIG. 14C is a mobile computer which comprises: a main body 1311; acamera section 1312; an image receiving section 1313; operation switches1314 and a display section 1315. The present invention can be applied tothe display section 1315 and other driver circuits.

FIG. 14D is a goggle type display which comprises: a main body 1316; adisplay section 1317; and an arm section 1318. The present invention canbe applied to the display section 1317 and other driver circuits.

FIG. 14E is a player using a recording medium which records a program(hereinafter referred to as a recording medium) which comprises: a mainbody 1319; a display section 1320; a speaker section 1321; a recordingmedium 1322; and operation switches 1323. This device uses DVD (digitalversatile disc), CD, etc. for the recording medium, and can performmusic appreciation film appreciation games and the use for Internet. Thepresent invention can be applied to the display section 1320 and otherdriver circuits.

FIG. 14F is a digital camera which comprises: a main body 1324; adisplay portion 1325; a view finder 1326; operation switches 1327; andan image receiving section (not shown in the figure). The presentinvention can be applied to the display section 1325 and drivercircuits.

FIG. 15A is a front type projector which comprises: a light sourceoptical system and a display device 1401; and a screen 1402. The presentinvention can be applied to the display section and other drivercircuits.

FIG. 15B is a rear type projector which comprises: a main body 1403; alight source optical system and a display device 1404; a mirror 1405;and a screen 1406. The present invention can be applied to the displaysection and other driver circuits.

As described above, the applicable range of the present invention isvery large, and the invention can be applied to electronic devices ofvarious areas. Note that the electronic devices of the presentembodiment can be achieved by utilizing any combination of constitutionsin Embodiment mode 1 to 4, Embodiments 1, 2 and 3.

According to the present invention, a first protective circuit, or acontact hole at an end of a first signal line of a pre-charge circuit,is used to reduce the energy of static electricity generated duringetching for opening contact holes in an interlayer insulating film,thereby preventing electrostatic discharge damage to a pixel TFT, adriving circuit TFT, and the pre-charge circuit.

By preventing electrostatic discharge damage, the present invention canimprove the yield and reliability of a semiconductor device and iseffective in reducing manufacture cost.

1. A semiconductor device comprising: a crystalline semiconductor islandformed on an insulating surface; an insulating film formed on thecrystalline semiconductor island; and a first signal line and a secondsignal line, each of which overlaps the crystalline semiconductor islandwith the insulating film interposed therebetween, wherein; the firstsignal line and the second signal line are connected to each otherthrough a metal wiring line, and the metal wiring line at leastpartially overlaps the crystalline semiconductor island.
 2. A deviceaccording to claim 1, wherein the first signal line and the secondsignal line are gate signal lines.
 3. A device according to claim 1,wherein the first signal line and the second signal line areelectrically connected to gate electrodes of thin film transistors in adriving circuit and a pixel region, respectively.
 4. A device accordingto claim 1, wherein the crystalline semiconductor island contains animpurity element giving an n type or a p type conductivity.
 5. A deviceaccording to claim 1, wherein the first signal line and the secondsignal line are spaced apart from each other so that the first signalline and the crystalline semiconductor island sandwich the insulatingfilm and the second signal line and the crystalline semiconductor islandsandwich the insulating film, respectively.
 6. A device according toclaim 5, wherein the first signal line and the second signal line aregate signal lines.
 7. A device according to claim 5, wherein the firstsignal line and the second signal line are electrically connected togate electrodes of thin film transistors in a driving circuit and apixel region, respectively.
 8. A device according to claim 5, whereinthe crystalline semiconductor island contains an impurity element givingan n type or a p type conductivity.
 9. A device according to claim 1,wherein said semiconductor device comprises at least one electric deviceselected from the group consisting of a video camera, a digital camera,a projector, a head mounted display, a car navigation system, a carstereo, a personal computer, a portable information terminal, a mobilecomputer, a portable telephone and an electronic book.
 10. Thesemiconductor device according to claim 1, the semiconductor devicefurther comprising a pixel region and at least one driving circuitportion, wherein: the crystalline semiconductor island, the insulatingfilm, the first signal line, and the second signal line togethercomprise a first protective circuit; and the first protective circuit isprovided between the driving circuit and the pixel region.
 11. A deviceaccording to claim 10, wherein said semiconductor device comprises atleast one electric device selected from the group consisting of a videocamera, a digital camera, a projector, a head mounted display, a carnavigation system, a car stereo, a personal computer, a portableinformation terminal, a mobile computer, a portable telephone and anelectronic book.
 12. The semiconductor device according to claim 10,wherein: the first protective circuit is provided between a secondprotective circuit and the pixel region.
 13. A device according to claim12, wherein said semiconductor device comprises at least one electricdevice selected from the group consisting of a video camera, a digitalcamera, a projector, a head mounted display, a car navigation system, acar stereo, a personal computer, a portable information terminal, amobile computer, a portable telephone and an electronic book.
 14. Asemiconductor device comprising: a semiconductor island formed over aninsulating surface; a first insulating film formed over thesemiconductor island; and a first signal line and a second signal line,each of which overlaps the semiconductor island with the firstinsulating film interposed therebetween, wherein: the first signal lineand the second signal line are connected to each other through a metalwiring line, and the metal wiring line at least partially overlaps thesemiconductor island.
 15. A semiconductor device according to claim 14,wherein the semiconductor island comprises a crystalline semiconductorisland.
 16. A semiconductor device according to claim 15, furthercomprising a second insulating film formed over the first and secondlines, wherein the metal wiring line is formed over the secondinsulating film.
 17. A semiconductor device according to claim 14,further comprising a second insulating film formed over the first andsecond lines, wherein the metal wiring line is formed over the secondinsulating film.
 18. A semiconductor device comprising: a first circuitcomprising: a semiconductor island formed over an insulating surface, afirst insulating film formed over the semiconductor island, a firstsignal line and a second signal line, each of which overlaps thesemiconductor island with the first insulating film interposedtherebetween, and a metal wiring line electrically connecting the firstsignal line and the second signal line; a second circuit comprising atransistor; and a third circuit comprising a transistor, wherein: thefirst signal line is connected to the second circuit and the secondsignal line is connected to the third circuit, and the metal wiring lineat least partially overlaps the semiconductor island.
 19. Asemiconductor device according to claim 18, wherein the second circuitis a pixel portion and the third circuit is a driving circuit fordriving the pixel portion.
 20. A semiconductor device according to claim18, wherein the second circuit is a pixel portion and the third circuitis a protective circuit.
 21. A semiconductor device according to claim18, wherein the first and second signal lines are gate signal lines. 22.A semiconductor device according to claim 18, wherein said semiconductordevice comprises at least one electric device selected from the groupconsisting of a video camera, a digital camera, a projector, a headmounted display, a car navigation system, a car stereo, a personalcomputer, a portable information terminal, a mobile computer, a portabletelephone and an electronic book.
 23. A semiconductor device accordingto claim 18, further comprising a second insulating film formed over thefirst and second signal lines, wherein the metal wiring line is formedover the second insulating film.
 24. A semiconductor device comprising:a crystalline semiconductor island formed on an insulating surface; aninsulating film formed on the crystalline semiconductor island; and afirst metal signal line and a second metal signal, each of whichoverlaps the crystalline semiconductor island with the insulating filminterposed therebetween, wherein the first metal signal line and thesecond metal signal line are connected to each other through a metalwiring line.
 25. A device according to claim 24, wherein the first metalsignal line and the second metal signal line are gate signal lines. 26.A device according to claim 24, wherein the first metal signal line andthe second metal signal line are electrically connected to gateelectrodes of thin film transistors in a driving circuit and a pixelregion, respectively.
 27. A device according to claim 24, wherein thecrystalline semiconductor island contains an impurity element giving ann type or a p type conductivity.
 28. A device according to claim 24,wherein the first metal signal line and the second metal signal line arespaced apart from each other so that the first metal signal line and thecrystalline semiconductor island sandwich the insulating film and thesecond metal signal line and the crystalline semiconductor islandsandwich the insulating film.
 29. A device according to claim 28,wherein the first metal signal line and the second metal signal line aregate signal lines.
 30. A device according to claim 28, wherein the firstmetal signal line and the second metal signal line are electricallyconnected to gate electrodes of thin film transistors in a drivingcircuit and a pixel region, respectively.
 31. A device according toclaim 28, wherein the crystalline semiconductor island contains animpurity element giving an n type or a p type conductivity.
 32. A deviceaccording to claim 24, wherein said semiconductor device comprises atleast one electric device selected from the group consisting of a videocamera, a digital camera, a projector, a head mounted display, a carnavigation system, a car stereo, a personal computer, a portableinformation terminal, a mobile computer, a portable telephone and anelectronic book.
 33. The semiconductor device according to claim 24, thesemiconductor device further comprising a pixel region and at least onedriving circuit portion, wherein: the crystalline semiconductor island,the insulating film, the first metal signal line, and the second metalsignal line together comprise a first protective circuit; and theprotective circuit is provided between the driving circuit and the pixelregion.
 34. A device according to claim 33, wherein said semiconductordevice comprises at least one electric device selected from the groupconsisting of a video camera, a digital camera, a projector, a headmounted display, a car navigation system, a car stereo, a personalcomputer, a portable information terminal, a mobile computer, a portabletelephone and an electronic book.
 35. The semiconductor device accordingto claim 33, wherein: the first protective circuit is provided between asecond protective circuit and the pixel region.
 36. A device accordingto claim 35, wherein said semiconductor device comprises at least oneelectric device selected from the group consisting of a video camera, adigital camera, a projector, a head mounted display, a car navigationsystem, a car stereo, a personal computer, a portable informationterminal, a mobile computer, a portable telephone and an electronicbook.
 37. A semiconductor device comprising: a semiconductor islandformed over an insulating surface; a first insulating film formed overthe semiconductor island; and a first metal signal line and a secondmetal signal line, each of which overlaps the semiconductor island withthe first insulating film interposed therebetween, wherein the firstmetal signal line and the second metal signal line are connected to eachother through a metal wiring line.
 38. A semiconductor device accordingto claim 37, wherein the semiconductor island comprises a crystallinesemiconductor island.
 39. A semiconductor device according to claim 38,further comprising a second insulating film formed over the first andsecond metal signal lines, wherein the metal wiring line is formed overthe second insulating film.
 40. A semiconductor device according toclaim 37, further comprising a second insulating film formed over thefirst and second metal signal lines, wherein the metal wiring line isformed over the second insulating film.
 41. A semiconductor devicecomprising: first circuit comprising: a semiconductor island formed overan insulating surface, a first insulating film formed over thesemiconductor island, a first metal signal line and a second metalsignal line, each of which overlaps the semiconductor island with thefirst insulating film interposed therebetween, and a metal wiring lineelectrically connecting the first metal signal line and the second metalsignal line; a second circuit comprising a transistor; and a thirdcircuit comprising a transistor, wherein the first metal signal line isconnected to the second circuit and the second metal signal line isconnected to the third circuit.
 42. A semiconductor device according toclaim 41, wherein the second circuit is a pixel portion and the thirdcircuit is a driving circuit for driving the pixel portion.
 43. Asemiconductor device according to claim 41, wherein the second circuitis a pixel portion and the third circuit is a protective circuit.
 44. Asemiconductor device according to claim 41, wherein the first and secondmetal signal lines are gate signal lines.
 45. A semiconductor deviceaccording to claim 41, wherein said semiconductor device comprises atleast one electric device selected from the group consisting of a videocamera, a digital camera, a projector, a head mounted display, a carnavigation system, a car stereo, a personal computer, a portableinformation terminal, a mobile computer, a portable telephone and anelectronic book.
 46. A semiconductor device according to claim 41,further comprising a second insulating film formed over the first andsecond metal signal lines, wherein the metal wiring line is formed overthe second insulating film.
 47. A semiconductor device comprising: acrystalline semiconductor island formed on an insulating surface; aninsulating film formed on the crystalline semiconductor island; and afirst signal line and a second signal, each of which overlaps thecrystalline semiconductor island with the insulating film interposedtherebetween, wherein: the first signal line and the second signal lineare connected to each other through a metal wiring line, and thecrystalline semiconductor island is interposed between the first signalline and the second signal line.
 48. A device according to claim 47,wherein the first signal line and the second signal line are gate signallines.
 49. A device according to claim 47, wherein the first signal lineand the second signal line are electrically connected to gate electrodesof thin film transistors in a driving circuit and a pixel region,respectively.
 50. A device according to claim 47, wherein thecrystalline semiconductor island contains an impurity element giving ann type or a p type conductivity.
 51. A device according to claim 47,wherein the first signal line and the second signal line are spacedapart from each other so that the first signal line and the crystallinesemiconductor island sandwich the insulating film and the second signalline and the crystalline semiconductor island sandwich the insulatingfilm, respectively.
 52. A device according to claim 51, wherein thefirst signal line and the second signal line are gate signal lines. 53.A device according to claim 51, wherein the first signal line and thesecond signal line are electrically connected to gate electrodes of thinfilm transistors in a driving circuit and a pixel region, respectively.54. A device according to claim 51, wherein the crystallinesemiconductor island contains an impurity element giving an n type or ap type conductivity.
 55. A device according to claim 47, wherein saidsemiconductor device comprises at least one electric device selectedfrom the group consisting of a video camera, a digital camera, aprojector, a head mounted display, a car navigation system, a carstereo, a personal computer, a portable information terminal, a mobilecomputer, a portable telephone and an electronic book.
 56. Thesemiconductor device according to claim 47, the semiconductor devicefurther comprising a pixel region and at least one driving circuitportion, wherein: the crystalline semiconductor island, the insulatingfilm, the first signal line, and the second signal line togethercomprise a first protective circuit; and the protective circuit isprovided between the driving circuit and the pixel region.
 57. A deviceaccording to claim 56, wherein said semiconductor device comprises atleast one electric device selected from the group consisting of a videocamera, a digital camera, a projector, a head mounted display, a carnavigation system, a car stereo, a personal computer, a portableinformation terminal, a mobile computer, a portable telephone and anelectronic book.
 58. The semiconductor device according to claim 56,wherein: the first protective circuit is provided between a secondprotective circuit and the pixel region.
 59. A device according to claim58, wherein said semiconductor device comprises at least one electricdevice selected from the group consisting of a video camera, a digitalcamera, a projector, a head mounted display, a car navigation system, acar stereo, a personal computer, a portable information terminal, amobile computer, a portable telephone and an electronic book.
 60. Asemiconductor device comprising: a semiconductor island formed over aninsulating surface; a first insulating film formed over thesemiconductor island; and a first signal line and a second signal line,each of which overlaps the semiconductor island with the firstinsulating film interposed therebetween, wherein: the first signal lineand the second signal line are connected to each other through a metalwiring line, and the semiconductor island is interposed between thefirst signal line and the second signal line.
 61. A semiconductor deviceaccording to claim 60, wherein the semiconductor island comprises acrystalline semiconductor island.
 62. A semiconductor device accordingto claim 61, further comprising a second insulating film formed over thefirst and second lines, wherein the metal wiring line is formed over thesecond insulating film.
 63. A semiconductor device according to claim60, further comprising a second insulating film formed over the firstand second lines, wherein the metal wiring line is formed over thesecond insulating film.
 64. A semiconductor device comprising: a firstcircuit comprising: a semiconductor island formed over an insulatingsurface, a first insulating film formed over the semiconductor island, afirst signal line and a second signal line, each of which overlaps thesemiconductor island with the first insulating film interposedtherebetween, and a metal wiring line electrically connecting the firstsignal line and the second signal line; a second circuit comprising atransistor; and a third circuit comprising a transistor; wherein: thefirst signal line is connected to the second circuit and the secondsignal line is connected to the third circuit, and the semiconductorisland is interposed between the first signal line and the second signalline.
 65. A semiconductor device according to claim 64, wherein thesecond circuit is a pixel portion and the third circuit is a drivingcircuit for driving the pixel portion.
 66. A semiconductor deviceaccording to claim 64, wherein the second circuit is a pixel portion andthe third circuit is a protective circuit.
 67. A semiconductor deviceaccording to claim 64, wherein the first and second signal lines aregate signal lines.
 68. A semiconductor device according to claim 64,wherein said semiconductor device comprises at least one electric deviceselected from the group consisting of a video camera, a digital camera,a projector, a head mounted display, a car navigation system, a carstereo, a personal computer, a portable information terminal, a mobilecomputer, a portable telephone and an electronic book.
 69. Asemiconductor device according to claim 64, further comprising a secondinsulating film formed over the first and second signal lines, whereinthe metal wiring line is formed over the second insulating film.